As mobile station users travel with their devices (e.g. mobile phones, mobile computers, and mobile broadband modems), a number of processes must take place to assure continuous service. One of the processes is idle handing off between mobile networks as users travel from region to region. The idle handoff process is important so the user has continuous service and stays on the correct system(s), as the user is being handed off from base station to base station. It can also cause problems for the mobile network provider if the handoff is performed improperly.
Currently, a list of System Identification Numbers “SID” and/or Network Identification Number (“NID”) combinations and radio frequency (“RE”) channels to scan are loaded into the mobile station. Once the mobile station is activated and is traveling, the RF channels are scanned until the appropriate SID/NID is found. The mobile station then registers on that mobile network.
To facilitate customer roaming where a particular operator may not have network coverage, the service provider or operator of one network will have agreements with other operators/service providers. Under such agreements, customers of the other operators may roam-in and use the one provider's network, whereas customers of the one provider may roam-out and use the networks of the other operators/service providers. However, different agreements among the parties may have different terms. As a result, some agreements may be more favorable, and a particular operator or service provider may ‘prefer’ for its customers to utilize the network of a particular other provider in certain areas. Hence, for a roaming subscriber, there is a financial benefit to the carrier selling service to the subscriber to implement procedures in the subscriber's mobile station to insure that the device selects the system in any area of operation that offers the best financial arrangement for services provided to the carrier's subscribers.
By way of a more specific example, the carrier may operate its network over a wide geographic area, and the carrier will have roaming agreements with operators of other networks in many other areas where subscribers roam. In some areas, the carrier may operate a network and have a roaming agreement with another carrier for instances in which a mobile station can not obtain access to the carrier's own network. In such a case, it is preferable for the subscriber's mobile station to select the carrier's network first, select the network of the roaming partner second and select any other available network only in the event that the first two network choices are inaccessible. In other areas, the carrier may have agreements with two operators of local networks. However, in such an area, one roaming agreement offers better rates, therefore the network of the preferred roaming partner should be selected whenever possible.
For the efficient acquisition of mobile communication networks, the carriers and their equipment vendors have developed and standardized a number of techniques for selecting systems in different areas for acquiring the network and obtaining service therefrom, in accordance with preferences of the subscriber's service provider/carrier. However, since the Third Generation Partnership Project 2 (3GPP2) and Third Generation Partnership Project (3GPP) standards bodies are working independently, the system selection procedures that they have established are different and use databases that are structured differently. 3GGP2 uses a Preferred Roaming List (PRL) that contains a table which identifies all of the operators that are roaming partners and which lists those partner operators in priority order. 3GPP uses Public Land Mobile Network (PLMN) lists to do the same.
Searching and acquiring a network, using a full PRL or PLMN search, however, takes considerable time and is typically done when a device is first turned-on or has lost all network service for some period of time. Each network listing in a typical preference list, e.g. in a PRL, might include a system ID (SID), a network ID (NID), a channel identification, and identification of a Radio Frequency Band, for each system and be classified by a geographic information index. The search may be time consuming, especially if a system has one or more configurable system parameters, and each such parameter can have one of multiple possible values. In this case, the station may perform acquisition for different possible combinations of values for the configurable system parameters in order to detect the system. Search and acquisition for a large number of possible combinations of parameter values from a long PRL or PLMN may extend search time and consume excessive battery power, both of which are undesirable.
For faster acquisition in other cases, for example, when the mobile device has been powered off briefly or in some cases when the device disconnects from one system while roaming, the device normally searches using a Most Recently Used (MRU) list having information of some much smaller number the most recently connected systems. The MRU list includes modes (CDMA, AMPS, EV-DO, etc.), band classes (Cellular, PCS, etc.) and channels of the most recently used systems. When an network is not found that matches a listing in the MRU list, the mobile device may turn to a more extensive search based on the PRL or PLMN. In this later case, if the device selects a new system, the device adds the system as a new entry in the MRU list for future use.
One of the disadvantages of these system selection techniques is that the mobile station may find a valid mobile network outside of the mobile network that the subscriber's carrier intends for the device to select for a user's current geographic coverage area. Mobile network providers are then required to configure the mobile network to redirect the mobile station while in idle mode. This redirection is not always practical and can reduce the capacity and/or the coverage of the existing mobile network.
For example, in a mobile network A, mobile stations are required to idle on channel 625 1900 MHz. However, in a mobile network B, bordering mobile network A, mobile stations can get on and idle on channel 384 850 MHz. This is not ideal since channel 384 850 MHz is used only in mobile network B and not mobile network A. Every channel 384 850 MHz from every antenna on every tower in mobile network B that transmits RF into mobile network A needs to have a parameter that redirects all mobile stations in order to make the mobile stations that acquire mobile network B channel 384 850 MHz reacquire mobile network A's channel 625 1900 MHz.
Alternately, a base station that needs to handle mobile calls on mobile network B channel 384 850 MHz and whose footprint extends into mobile network A, may not have a redirect parameter equipped. Thus, the coverage of the base station needs to be curtailed until it is not broadcasting into mobile network A. This may limit the call quality in the intended coverage area.
Mobile stations can idle on valid channels outside of the intended coverage area due to improper mobile network border configuration. This leads to the occurrence of dropped calls or failed call attempts. Service areas are limited to SID/NID broadcasts which are transmitted over RF. The service areas are actually geographically determined but controlled by RF. RF is inherently difficult to control. The granularity of the system is limited to a combination SID/NID/Channel selections.
In several prior patents, Dennison et al. (hereinafter “Dennison”), U.S. Pat. Nos. 5,235,633; 5,546,445; and 6,324,404, describe a solution to a similar problem. In Dennison, the mobile station determines its location using a process (e.g. a GPS built into the mobile station) to determine its exact geographic location (EGL). The mobile station then transmits its EGL up to the mobile network site. The EGL is compared to a database of the geographic boundaries prescribed for each mobile network site, the proper mobile network site for the particular user is determined, and the mobile network site informs the mobile station which mobile network site will handle a call.
Thus, the mobile network learns of the mobile station's location. Then the mobile network (e.g. a mobile telephone switching office or MTSO) tells the mobile station which mobile network site or channel to acquire. The downfall to this system is that it requires communication with, and processing by, the mobile network base station/mobile network switching office. This solution can tax the mobile network and the mobile network based systems with directing each of many mobile stations that needs to rectify its position. This solution also reduces the capacity of a cells site since the carrier can't be used partially for traffic and partially for redirection, it's either one or the other.
Hence, a need exists for a system that will allow mobile stations to properly place themselves on the proper mobile network base station or frequency (channel) without the need to acquire or communicate to a mobile network system.